1. Field of the Invention
The present invention relates to an apparatus for and method of performing an automatic cleaning of nuclear fuel-cladding tubes, more specifically to an apparatus for and a method of automatically cleaning nuclear fuel-cladding tubes, in which a cleaning material is automatically prepared and sprayed to efficiently clean the inside of the nuclear fuel-cladding tube.
2. Background of the Related Art
Nuclear fuel is manufactured under high temperature and pressure conditions using uranium compounds. The nuclear fuel is enclosed by aluminum or magnesium cladding such nuclear waste generated from nuclear fission is prevented from being mixed with coolant and leaked to the outside. In case of a PWR (pressurized water reactor), a low-enriched uranium dioxide powder is compacted and sintered into cylindrical yellowish brown pallets, which are stacked one on another inside a thin tube made of zircaloy (Zr—Sn alloy containing a light amount of Cr and Fe) and both ends of the tube are sealed. This metallic tube containing fuel pallets stacked thereinside is called a “fuel rod”, and the tube is called a fuel cladding tube.
The fuel rod is loaded into a structure to form a fuel bundle assembly. In case of the fuel for the Korean Standard Nuclear Power Pant, about 177 fuel bundle assemblies are loaded into the reactor and used for around 4 years. This fuel rod is a core component of the nuclear fuel, and the cladding tube for this fuel rod must be treated and maintained under very clean environment.
However, before nuclear fuel pellets are put into the cladding tube, the cladding tube may contain dust, stain, moisture or the like thereinside. In this case, these may affect operation of the nuclear reactor. In particular, in case of moisture, it is decomposed into hydrogen, which may affect the nuclear fission reaction, and thus the moisture must be removed.
Therefore, a cladding tube cleaning must be performed during the manufacturing process for nuclear fuel rods.
In the conventional cleaning process, an appropriate amount of cladding tubes are put on a working station and a worker inserts manually a wool plug wet with ethyl alcohol into the inside of a cladding tube using tweezers and moves up and down the plug. Alternatively, an air gun is used to blow a compressed air to carry out a primary internal cleaning, and then a dry sponge of hexagonal shape is inserted and manually moved back and forth or a compressed air is blown using an air gun to thereby perform a secondary internal cleaning.
In addition, even after the cladding tube cleaning is completed, if a cleaning material remains inside the cladding tube, an accident may be caused. Thus, a visual inspection must be required for the cleaned cleaning tube.
On the other hand, Korean Patent No. 10-0446351 discloses an apparatus for cleaning a cladding tube after use. In this patent, a rotating brush is inserted into the inside of a cladding tube to clean the inside thereof. However, the above technology is not directed to cleaning a cladding tube before use. In addition, this technology is not automated and thus cannot perform a rapid cleaning of a large amount of cladding tubes.
Considering the productivity of nuclear fuel, as many as about 1200 cladding tubes must be cleaned a day. Therefore, in case where a cleaning material is manually pushed into the inside of a cladding tube and an air gun is used to clean the tube, a large quantity of time is required to thereby unable to clean a massive amount of tube and degrade the productivity, and also cause a risk of occurrence of musculoskeletal disease due to the repeated manual work.
The above conventional method of manually cleaning a cladding tube embraces many disadvantages and problems as follows. Firstly, during the process, a cleaning material charge and discharge consumes a lot of time to thereby extend the process time and degrade the efficiency and productivity. Secondly, the tube inspection process after cleaning must be performed one by one for every single cladding tube. Thirdly, the cladding tube must be manually transferred to each working place and the above jobs all must be manually carried out, thereby leading to excessive use of muscles and joints of workers, which may cause diseases in the musculoskeletal systems.